This application is a national stage of PCT/EP98/08323 filed Dec. 18, 1998 and based upon DE 198 03 588.8 filed Jan. 30, 1998 under the International Convention.
1. Field of the Invention
The invention concerns a process and a device for readout radiation image information stored on an image medium, in particular a phosphorus storage plate coated with a crystalline storage substance, imaged by exposure to high energy radiation.
2. Description of the Related Art
In known devices of this type an image medium for receiving a radiation image is radiated for example in an electron microscope, and is then optically read in a separate readout device by scanning under luminescence-excitation. The utilized image medium have a high dynamic, however the image quality is compromised by inhomogeneities in the image layer. One problem is comprised therein, that images of different scans have a displacement or offset with respect to each other as a rule on the basis of differing orientations of the image medium in the reading device. A further problem is comprised in the unambiguous identification of the individual employed image plates.
Beginning therewith, it is the task of the invention to improve a process and a device of this type, such that the radiation image information can be read out reliably and with low affliction of errors. A high quality should also be guaranteed, especially in the case of high radiation intensities wherein static noise artifacts occur in the background as opposed to systematic errors on the basis of image medium inhomogeneities.
The invention is based on the discovery, that the light reflected from the image medium can be correlated with the luminescence light and therewith can be used complimentary or supplementary for evaluating the radiation image information. In accordance therewith, it is envisioned for the process aspect of the solution of the above-mentioned task, that during scanning of the image plate, the reflectioned readout light is continuously monitored as a reflection signal, and the reflection signal is converted into digital reflection values in synchrony with the image signal. Therewith, the detected values can be clearly associated and be evaluated with respect to correlation. Generally, from the processing of the reflection light, there results an information gain, which in the end makes possible a substantial increase in the range of employment of the image media.
A particularly advantageous aspect is comprised therein, that the image values for obtaining the radiation image information allow themselves to be corrected in accordance with the magnitude of the reflection value. This can generally occur by determining from the reflection value the correction value to be associated with the image points, and that the image value is scaled or graduated image-point-wise with the correction value.
It is further of particular advantage, when a reference image is produced by a homogenous surface radiation of the image medium. Therewith it is above all possible to clearly determine correlations between the parallel determined image- and reflection value by a one-time measurement, and to utilize this for correction or as the case may be processing of various non-homogenous working images. Advantageously correlation data (ak,K) are thereby determined from the image values BR(z,xcfx86) and reflection values RR(z,xcfx86) of the reference image, and the image values B(z,xcfx86) of a working image are corrected according to the values from the stored correlation data (ak,K) associated reflection values R(z,xcfx86).
It is particularly advantageous when the correlation data from the image and reflection values of the reference image are determined in the Fourier area. For this the variance of the values
Bxe2x80x2R(z,xcfx86)=BR(z,xcfx86)xc2x7[akxc2x7F2xe2x88x921{F2{RR(z,xcfx86)}xc2x7K(u,v)}]xe2x88x921
are minimized, wherein Bxe2x80x2R refers to the corrected image value of the reference image, ak refers to a correlation factor to be varied, K(u,v) corresponds to varying correlation coefficients in the Fourier area, F2 corresponds to a two-dimensional Fourier transformation and F2xe2x88x921 corresponds to the inverse transformation. With the correlations determined in this manner the image values B(z,xcfx86) can be corrected from the working images in accordance with the equation or relationship
Bxe2x80x2(z,xcfx86)=B(z,xcfx86)xc2x7[akxc2x7F2xe2x88x921{F2{RR(z,xcfx86)}xc2x7K(u,v)}]xe2x88x921
wherein Bxe2x80x2(z,xcfx86) corresponds to the corrected image value of the working image, ak and K(u,v) corresponds to the determined and the stored correlation data, F2 corresponds to the two dimensional Fourier transformation and F2xe2x88x921 refers to the inverse transformation.
A further advantageous aspect of the reflection signal evaluation is comprised therein, that a working and a reference image can be correlated to each other with respect to common scanning coordinates. Therewith the various possible fixing positions of the image medium in the read-out device can be mathematically taken into account, so that an image correction on the basis of previously determined data with respect to given image point coordinates is possible. For this it is advantageous, by cross-correlation of the reflection values R, RR of a working and a reference image, to determine the translation vector {right arrow over (r)} and rotation angle xcex1 of a one-to-the-other associated image points of the working and the reference image mapped coordinate transformation.
A doubled correction with respect to the errors from inhomogeneities is made possible thereby, that from the image values B, BR of a working and a reference image according to the measurement of the associated reflection values R,RR corrected image values Bxe2x80x2,Bxe2x80x2R are produced, the corrected image values Bxe2x80x2,Bxe2x80x2R to are rectified each other, and the rectified or aligned corrected image values Bxe2x80x3 of the working image are scaled or graded with the rectified or aligned corrected image values Bxe2x80x3R of the reference image.
A further advantageous aspect of the reflection light determination is comprised therein, that by comparison of the reflection values R of a working image with stored reflection values RR of reference images of varying image mediums the particular image medium employed for recording the working image can be identified on the basis of positionally correlated inhomogeneities of the storage layer.
In respect to a device, it is proposed to solve the inventive task by providing in the reading/processing device a second photo-detector for sensing the readout light reflected by the image medium during scanning, and a second analog/digital converter for converting this starting signal into a digital reflection value R(z,xcfx86). The two channel determination makes possible an evaluation of the correlation between the luminescence and the reflection light signal. In order to clearly associate the digitized value of the two channels to each other, a clock pulse generator is provided for synchronized controlling of the two analog/digital converters. Therewith one working and one reflection value can be produced at the same time at each clock pulse signal and via the instantaneous scanning coordinates an image point can be fixed.